Defining critical speed

You can define critical speed functions to specify different radii. With each of these radii, a critical speed applies for the vehicle. These values are used to calculate the lateral drift speed and the lateral deviation of the vehicle due to excessive speed. (Using lateral drift speed).

In the Vehicles in the network list, you can display the Lateral deviation (excessive speed) of the vehicle (Displaying vehicles in the network in a list).

1.  On the Base Data menu, click > Functions > Critical speed.

The list of defined objects for the base data type opens.

By default, you can edit the list (Using lists).

2.  In the list on left, on the toolbar, click the Add button .

3.  In the Name table field, enter a name for the function.

4.  Repeat the following steps for the desired number of data points.

5.  In the list on right, on the toolbar, click the Add button .

6.  Enter the desired data.

Element Description

x

Curvature radius: Threshold value from which the Critical speed y of a vehicle can trigger a lateral deviation (critical speed), if a) the vehicle is driving on a link that traverses a 3D point and b) the Radius attribute of this point corresponds to the Curvature radius x (Attributes of links). Thereby the following applies:

  • Vissim takes into account the last 3D point passed as well as the next downstream 3D point of the link or connector on which the vehicle travels, if the radius at both points is > 0.
  • These two points can also be the first or the last point of the link or connector.
  • If both points have a different radius, Vissim uses the smaller value.
  • If the vehicle has passed the first of the two points but cannot reach the second because its vehicle route ends upstream of this point or, in the case of dynamic assignment, the path of the vehicle ends at a parking lot upstream of this point, Vissim will still use the radius of this second point even though the vehicle will not reach it.
  • Vissim calculates a speed quotient for the function Lateral drift speed (Using lateral drift speed).

y

Critical speed: Speed [m/s] for the given Curvature radius x.

The function value is linearly interpolated between several interpolation points.

The affected vehicle determines in each time step whether its maximum speed within the time step is above the critical speed. The smaller radius of the previous and next 3D point of the link are taken into account. Understeer can only occur if both 3D points have a radius > 0. The vehicle is carried out of the bend at the calculated lateral speed. If at the same time a deflection in the same direction is greater and the deflection is in the same direction, it affects the lateral movement.

The vehicle attribute Lateral deviation (overspeed) indicates the lateral deviation in the current time step (Displaying vehicles in the network in a list).

You assign the function Critical speed as an attribute to those vehicle types you wish to impact (Attributes of vehicle types).

Superordinate topic:

Defining functions for acceleration, deceleration and speed